Introduction to Chemistry

• Chemistry is the study of matter and its properties, as well as how matter changes.
• It's a natural science that deals primarily with atoms and molecules and their interactions.

Matter

• Matter is anything that has mass and occupies space (volume).
• It exists in different states, most commonly solid, liquid, and gas, but also plasma.

Chemical Elements

• A chemical element is a pure substance that consists only of atoms that have the same number of protons in their nuclei.
• Each element is characterized by its atomic number (number of protons).
• Elements are organized in the periodic table.

Chemical Compounds

• A chemical compound is a substance formed from two or more elements chemically bonded together in a fixed ratio.
• These bonds can be ionic or covalent.

Chemical Reactions

• Chemical reactions involve the rearrangement of atoms and molecules to form new substances.
• They are represented by chemical equations.
• These reactions involve the breaking and forming of chemical bonds.

Chemical Equations

• Chemical equations are symbolic representations of chemical reactions.
• Reactants are written on the left side, and products are written on the right side, separated by an arrow.
• Example: 2 H₂ + O₂ → 2 H₂O (Hydrogen reacts with oxygen to form water)

Balancing Chemical Equations

• Balancing ensures that the number of atoms of each element is the same on both sides of the equation.
• This adheres to the law of conservation of mass.
• Balancing is achieved by using coefficients in front of the chemical formulas.

Types of Chemical Reactions

• Synthesis (Combination): Two or more reactants combine to form a single product (A + B → AB).
• Decomposition: A single reactant breaks down into two or more products (AB → A + B).
• Single Displacement (Substitution): One element replaces another in a compound (A + BC → AC + B).
• Double Displacement (Metathesis): Ions are exchanged between two compounds (AB + CD → AD + CB).
• Combustion: A substance reacts rapidly with oxygen, producing heat and light.

Stoichiometry

• Stoichiometry deals with the quantitative relationships between reactants and products in a chemical reaction.
• It involves using balanced chemical equations to calculate the amounts of reactants and products involved in a reaction.
• Mole concept is central to stoichiometric calculations (1 mole = 6.022 x 10²³ entities).

Limiting Reactant

• The limiting reactant is the reactant that is completely consumed first in a chemical reaction.
• It determines the maximum amount of product that can be formed.
• The other reactants are considered in excess.

Yield

• Theoretical Yield: The maximum amount of product that can be produced from a given amount of limiting reactant based on stoichiometric calculations.
• Actual Yield: The amount of product actually obtained from a chemical reaction.
• Percent Yield: (Actual Yield / Theoretical Yield) x 100%

Acids and Bases

• Acids are substances that donate protons (H⁺) or accept electrons.
• Bases are substances that accept protons or donate electrons.
• pH scale measures the acidity or basicity of a solution (pH < 7 is acidic, pH > 7 is basic, pH = 7 is neutral).

Oxidation-Reduction (Redox) Reactions

• Oxidation is the loss of electrons.
• Reduction is the gain of electrons.
• Oxidation and reduction always occur together.
• Oxidizing agents cause oxidation and are reduced themselves.
• Reducing agents cause reduction and are oxidized themselves.

Reaction Rates

• Reaction rate is the speed at which a chemical reaction occurs.
• It is affected by factors such as:
  • Concentration of reactants
  • Temperature
  • Presence of catalysts
  • Surface area of solid reactants

Chemical Equilibrium

• Chemical equilibrium is the state in which the rate of the forward reaction equals the rate of the reverse reaction.
• At equilibrium, the concentrations of reactants and products remain constant.
• Le Chatelier's Principle: If a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress.
• Changes include:
  • Concentration
  • Temperature
  • Pressure